Some computer devices, which execute an application program on an operating system, execute plural application programs in parallel and display plural windows, each of which corresponds to an application program, as user interface. For example, JP-A-2004-94423 discloses a method for controlling plural windows.
According to a system in JP-A-2004-94423, under a condition that a first window and a second window are displayed, if a user expands the first window and a border of the first window touches the second window, the second window is moved so as to not overlap the first window. If the second window cannot be moved so as to not overlap the first window, the size of the second window is shrunk with an increase in size of the first window. In this way window overlap is prevented, and a user is able to view plural windows simultaneously.